1-70
Serial I/O3
When writing “1” to the serial I/O initialization bit of the serial
I/O3 control register 1, serial I/O3 is enabled, but each register
is not initialized. Set the value of each register by program.
A serial I/O3 interrupt request occurs when “0” is written to the
serial I/O initialization bit during an operation in automatic trans-
fer serial I/O mode. Disable the interrupt enable bit as necessary
by program.
A-D Converter/D-A Converter
The A-D/D-A conversion register functions as an A-D conversion
register during a read and a D-A conversion during a write. Ac-
cordingly, the D-A conversion register set value cannot be read
out.
The comparator for A-D converter uses capacitive coupling am-
plifier whose charge will be lost if the clock frequency is too low.
Therefore, make sure that f(XIN) is at least on 500 kHz during an
A-D conversion.
Do not execute the STP or WIT instruction during an A-D con-
version.
Instruction Execution Time
The instruction execution time is obtained by multiplying the fre-
quency of the internal clock
φ by the number of cycles needed to
execute an instruction. The number of cycles required to execute
an instruction is shown in the list of machine instructions.
The frequency of the internal clock
φ is half of the XIN frequency.
Data Link Layer Communication Control
The data link layer communication control circuit stops after a
reset. To restart or change modes, write “00XXXXX12” to the
communication mode register. Note that bits 4 and 5 are read-
only bits.
The P75/BUSOUT pin operates as a general-purpose pin after
release from reset. As a general-purpose port, its input/output
can be switched by the direction register.
Clock Changes
Use the LDM, STA, etc. instructions to modify the division ratio
of internal system clock
φ. (Do not use read-modify-write instruc-
tions such as CLB, SEB, etc.)
Do not modify the division ratio of the internal system clock until
the mode has been changed. For details concerning the number
of cycles necessary to change modes, refer to the clock section
in the explanation of about function blocks.
Use the LDM, STA, etc., instructions to clear interrupt request
bits assigned to the interrupt source discrimination register 1,
the interrupt source discrimination register 2, the transmit status
register, or the receive status register. (Do not use read-modify-
write instructions such as CLB, SEB, etc.)
Before executing the CLI or RTI instruction during an interrupt
processing routine, use the LDM or STA instruction to clear the
interrupt request bits of interrupt source discrimination registers
which have completed the interrupt processing.
If switching the mode between low-speed and double-speed,
switch the mode to middle/high-speed first, and then switch the
mode to double-speed by program. Do not switch the mode
from low-speed to double-speed directly. 1 to 4 machine cycles
are required for switching from low-speed mode to other mode.
Insert “clock switch timing wait” for switching the mode to
middle/high-speed, and then switch the mode to double-speed.
Table 10 lists the recommended transition process for system
clock switch.
Figure 74 shows the program example.
Table 10 Clock switch combination
Recommended transition process
Low-speed
→High-speed
Low-speed
→Middle-speed
Double-speed
→High-speed
Double-speed
→Middle-speed
Double-speed
→Low-speed
Middle-speed
→High-speed
Middle-speed
→Middle-speed
Middle-speed
→Low-speed
High-speed
→Double-speed
High-speed
→MIddle-speed
High-speed
→Low-speed
Fig. 74 Program example
Low-speed mode
→ Middle/High-speed mode → Double-speed mode switch
LDM xx, CPUM Low-speed mode
→ Middle/High-speed mode switch
NOP
Clock switch timing wait
NOP
(1 to 4 machine cycles are required for switching mode.)
LDM yy, CPUM Switch mode to double-speed
Note: CPUM = CPU mode register (address 003B16)
3874 Group User’s Manual
HARDWARE
NOTES ON PROGRAMMING